By now, most developers within the Drupal community have heard of the many tools and techniques used to improve Drupal performance such as varnish, memcache, solr, apc, ESI, etc. However, each comes with its own added complexity and administrative cost, so without knowing exactly what your performance bottleneck is, they can potentially do more harm than good.
Modules like Devel provide detailed information about queries being run on a particular request, but what if the time spent querying the database is only a small fraction of your overall pageload time? Profiling is the fastest, easiest way to get the data you need to make smart decisions about performance and scalability improvements.
In this session I'll demonstrate how to use the Devel module with the XHProf php extension to profile your Drupal site, how to interpret the data to find performance bottlenecks, and how to make it a part of your daily developing workflow.